Crystal structure of (E)-N-(4-bromophenyl)-2-cyano-3-[3-(2-methylpropyl)-1-phenyl-1H-pyrazol-4-yl]prop-2-enamide

The two independent molecules of C23H21BrN4O are closely similar and roughly planar except for the isopropyl groups. They are connected by hydrogen bonds of the types Namide—H⋯N≡C, Hphenyl⋯O=C and Hphenyl⋯Br.

In this article, we report the synthesis of the title compound 7, which bears a substituted acrylamide side chain at the 4-position of the pyrazole ring, by the reaction between 2-[(3isobutyl-1-phenyl-1H-pyrazol-4-yl)methylene]malononitrile 3 and N-(4-bromophenyl)-2-cyanoacetamide 4 in an ethanolwater mixture in the presence of sodium hydroxide (see Fig. 1, where the suggested mechanism is also shown).The reaction starts by the nucleophilic attack of the active methylene group of 4 at the double bond of 3 to give an intermediate Michael addition product 5, which eliminates malononitrile to give the final product 7.The structure of 7 was confirmed via spectroscopic techniques; thus, the IR spectrum indicated the presence of a characteristic NH absorption band at 3455 cm À 1 , and the 1 H NMR spectrum revealed the presence of an NH signal at 10.36 ppm, a singlet vinylic signal at 8.10 ppm, and aromatic protons at 7.52-7.63ppm.It is possible that compound 7 is the thermodynamically controlled product because of lower steric hindrance, and is thus formed instead of the N-aryl-2-pyridone 8 via intermediate 6.The structure of compound 7 has now been been unambiguously confirmed by single-crystal X-ray diffraction and is presented here.

Structural commentary
The structure of compound 7 is shown in Fig. 2, with selected molecular dimensions in Table 1 (and hydrogen bonds in Table 2); there are two independent molecules in the asymmetric unit.The configuration at the double bond C10 C11 is E, with the amide and pyrazolyl groups mutually trans, which leads to short intramolecular contacts H10� � �O1 of 2.43, 2.44 A ˚.The two independent molecules are linked to form a Figure 1 The reaction scheme leading to the title compound 7.

Figure 2
The structure of compound 7 in the crystal; two independent molecules are linked by hydrogen bonds (shown as dashed lines).Ellipsoids represent 50% probability levels.
dimer by hydrogen bonds of the type N amide -H� � �N C; the graph set is R 2 2 (12).The atom numbering of both molecules is the same, but with the addition of primes ( 0 ) for the second molecule.The centre of gravity of the asymmetric unit lies close to the point (0.5, 0.75, 0.5).
Bond lengths and angles may be considered normal, although the narrow angles in the pyrazole rings are necessarily reflected in some wide exocyclic angles, and the angle C4-C10-C11 is also wide.A least-squares fit of both molecules (for all atoms except hydrogens; Fig. 3) gave an r.m.s.deviation of 0.12 A ˚, with minor differences in the orientations of the isopropyl groups and the ring C14-19 (the latter involving torsion angle differences of ca 13 � ).This corresponds to the presence of a local twofold axis passing through the centre of gravity of the asymmetric unit.A side view of molecule 1 shows that it is very roughly planar except for the isopropyl group (Fig. 4).The interplanar angles between the pyrazole ring and rings C14-C19 and C20-C25, respectively, are 10.4 (2), 22.5 (2) � in molecule 1 and 10.3 (2), 8.9 (2) � in molecule 2. Another factor associated with the lack of planarity is the central torsion angle of the atom sequence C4-C10-C11-C12-N4-C20, which differs by ca 24 � from the 180 � required for an ideally extended sequence.The geometry at the amide nitrogen atoms is almost exactly planar (r.m.s.deviations from the best plane through the nitrogen and its immediate substituents are 0.012 and 0.004 A ˚for the two molecules).

Supramolecular features
The association of the two independent molecules to form a hydrogen-bonded dimer was discussed in the previous section.The common hydrogen-bonding pattern for amides, with dimer formation via two N-H� � �O C bonds, is not observed; this would require rotation around the amide C4-N12 bond to make the sequence O1 C12-N4-H4 synperiplanar rather than antiperiplanar, which would presumably involve a close approach of the bromophenyl and nitrile groups.There are also two pairs of 'weak' hydrogen bonds, namely H15� � �O1 0 /H15 0 � � �O1 and H16� � �Br1 0 / H16 0 � � �Br1 (for details see Table 2).The former link the dimers to form a ribbon structure parallel to the b axis (Fig. 5

Figure 3
A least-squares fit of both independent molecules.The second independent molecule is indicated by dashed green bonds.

Figure 4
Side view of molecule 1 (hydrogen atoms omitted).whereas the latter are associated with a ribbon structure parallel to the c axis (Fig. 6).The combination of the two ribbons leads to the final three-dimensional packing.

Database survey
The search employed the routine ConQuest (Bruno et al., 2002), part of Version 2023.3.0 of the Cambridge Database (Groom et al., 2016), and sought structures with pyrazole rings substituted at C4 by the group -C C(CN)-C( O)-N.
Only one exact hit was registered: Kariuki et al., 2022), which has a thiophenyl group instead of the isobutyl group in 7, and an unsubstituted amide group.It too shows the E configuration; the hydrogen bonding involves hydrogen-bonded dimers via N-H� � �O C contacts between the two independent molecules, crosslinked by further hydrogen bonds N-H� � �N C.There were, however, four other hits in which the substituent was involved in another ring fused with the pyrazole, e.g.Ali et al., 2013).

Data collection and reduction
Most crystals were fine needles that diffracted very weakly.However, a few broader laths were found, one of which was used for the data collection despite its somewhat diffuse reflection form.The reflections found in the initial cell determination were 93% indexed using a C-centred monoclinic cell with approximate cell constants a = 35.16,b = 12.77, c = 9.22 A ˚, � = 97.3� .During the course of the data collection, this was automatically changed to the final triclinic cell, presumably on the basis of a prohibitively high R int value for the monoclinic cell.A closer inspection of the complete data then revealed the twinning, and the data reduction was repeated accordingly.
around c*), whereby the relative volume of the smaller component refined to 0.2500 (8).The two largest peaks in the residual electron density (ca 1.4 e A ˚À 3 ) are arithmetically related to the coordinates of the two bromine atoms and are probably attributable to residual twinning effects.As is often the case for non-merohedral twins, some intensities were badly in error; six such reflections were omitted from the refinement.Because of the special methods involved in the data reduction of non-merohedral twins, equivalent reflections were merged and R(int) is thus meaningless; because reflections from both twinning components are included, the number of reflections should be interpreted with caution.The weighting parameters did not converge, but oscillated over a small range (e.g. the SHELXL 'a' parameter between 0.0504 and 0.0507); arbitrarily, we chose the former value.Crystal data, data collection and structure refinement details are summarized in Table 3.
The hydrogen atoms of the NH groups were refined freely, but with the N-H distances restrained to be approximately equal (command 'SADI').The methyl groups were included as idealized rigid groups allowed to rotate but not tip (command 'AFIX 137'), with C-H = 0.99 A ˚and H-C-H = 109.5� .Other hydrogen atoms were included using a riding model starting from calculated positions (C-H methylene = 0.99, C-H methine = 1.00,C-H arom = 0.95 A ˚).The U(H) values were fixed at 1.5 � U eq of the parent carbon atoms for the methyl group and 1.2 � U eq for other hydrogens.

Figure 5
Figure 5Packing diagram of compound 7 viewed parallel to the a axis.The dashed bonds indicate classical (thick) or 'weak' (thin) hydrogen bonds.For clarity, the bromophenyl rings have been reduced to their ipso carbon atoms and the isopropyl groups are omitted, as are the hydrogen atoms not involved in hydrogen bonding.

Figure 6
Figure 6 Packing diagram of compound 7 viewed parallel to the b axis.The dashed bonds indicate classical (thick) or 'weak' (thin) hydrogen bonds.For clarity, the isopropyl groups are omitted, as are the hydrogen atoms not involved in hydrogen bonding.

Table 3
Experimental details.
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